Method and apparatus for minimizing noise on a power supply line of a mobile radio

ABSTRACT

An apparatus and method are provided for minimizing noise on a power supply line ( 105 ) of a mobile radio, such as generated in a vehicular environment. An adaptive power supply conditioner ( 100 ) detects unwanted noise on the vehicle&#39;s power supply line ( 105 ) and via the use of an adaptive noise canceller ( 140 ), generates a cancellation signal ( 145 ) having the same amplitude but opposite phase of the input signal&#39;s detected noise. The cancellation signal ( 145 ) is fed forward and combined with the power supply line ( 105 ) in order to minimize unwanted noise on the supply line ( 105 ) leading to the mobile radio. The conditioner&#39;s output ( 165 ) is checked for further error and is fed back to the adaptive noise filter ( 140 ) for further filtering and the generation of an updated cancellation signal based on current noise conditions.

FIELD OF THE INVENTION

The present invention generally relates to mobile radios and moreparticularly to the minimization of power supply ripple or noise foundon raw DC input supply line to the mobile radio mounted in motorvehicles.

BACKGROUND

Mobile radios mounted in cars, motorcycles, trucks or other vehicles arepowered by the vehicle's main power supply. A main power supply line isrun throughout the vehicle to power electromechanical components inaddition to the mobile radio. The main power supply line is oftensubjected to unwanted noise, commonly referred to as power supply rippleor alternator whine. The intensity of alternator induced radio noiseincreases and decreases with changes in engine speed. The noise may alsobe caused by the noisy electrical and thermal environment in thevehicle.

Conventional approaches to addressing unwanted noise on the supply lineinclude the use of ripple regulators. These ripple regulators utilizecapacitors, inductors and transistors for forming passive filters thatblock the ripple noise on the supply line. However, the low-frequencyfilter bandwidth required for these filters can only be realized by theuse of large capacitors and inductors. This makes these approachesundesirable for applications where size and/or weight are importantfactors. Furthermore, the parasitic capacitance and inductance oftransistors leads to timing delays in the components of the regulator.As a result, the output of the regulator may overshoot or undershoot thedesired output. Heating of capacitors and inductors is another cause ofconcern in such regulators.

Other approaches to overcome the power supply noise problem haverequired significant hardware additions that draw additional current andmay result in a voltage drop on the power supply line. Feedback controltechniques that have been used in the past tend to introduce thepotential for instability and oscillation, thereby putting more noise onthe power supply line.

Accordingly, it would be desirable to have an improved method andapparatus to address unwanted noise on the power supply line,particularly as applied to powering a mobile radio in a vehicularenvironment. It would be further desirable to have an improved methodand apparatus with reduced power requirement.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separate viewsand which together with the detailed description below are incorporatedin and form part of the specification, serve to further illustratevarious embodiments and to explain various principles and advantages allin accordance with the present invention.

FIG. 1 is a block diagram of a power supply conditioner for a mobileradio formed accordance with an embodiment of the invention;

FIG. 2 is a flowchart of a method for minimizing noise on a supply lineof a mobile radio in accordance an embodiment of the invention;

FIG. 3 is a schematic of a simplified power supply conditioner inaccordance with some embodiments of the invention;

FIG. 4 is an example of a graph of power supply line input in accordancewith some embodiments of the invention;

FIG. 5 is an example of a graph of simulated output for the power supplyconditioner in accordance with some embodiments of the invention; and

FIG. 6 is an example of a power interface device in accordance with someembodiments of the invention.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions of some of the elements inthe figures may be exaggerated relative to other elements to help toimprove understanding of embodiments of the present invention.

DETAILED DESCRIPTION

Before describing in detail embodiments that are in accordance with thepresent invention, it should be observed that the embodiments resideprimarily in an apparatus and method for cancelling noise on a powersupply line leading to a mobile radio mounted in a vehicle. The powersupply conditioner of the present invention provides improved noisereduction via the use of adaptive filtering. Accordingly, the apparatusand method components have been represented where appropriate byconventional symbols in the drawings, showing only those specificdetails that are pertinent to understanding the embodiments of thepresent invention so as not to obscure the disclosure with details thatwill be readily apparent to those of ordinary skill in the art havingthe benefit of the description herein.

In this document, relational terms such as first and second, and thelike may be used solely to distinguish one entity or action from anotherentity or action without necessarily requiring or implying any actualsuch relationship or order between such entities or actions. The terms“comprises,” “comprising,” or any other variation thereof, are intendedto cover a non-exclusive inclusion, such that a process, method,article, or apparatus that comprises a list of elements does not includeonly those elements but may include other elements not expressly listedor inherent to such process, method, article, or apparatus. An elementproceeded by “comprises . . . a” does not, without more constraints,preclude the existence of additional identical elements in the process,method, article, or apparatus that comprises the element.

FIG. 1 is a block diagram of a power supply conditioner 100 for a mobileradio 101 in accordance with an embodiment of the invention. Powersupply conditioner 100 is preferably incorporated within the mobileradio 101. A main power supply (A+) 102, typically the vehicle battery,powers a plurality of electromechanical components within the vehicleincluding mobile radio 101. Mobile radio 101 receives power from themain power supply 102 via a power supply line 105, which as discussedpreviously, can be subjected to unwanted noise generated thereon fromother electromechanical components. In accordance with the presentinvention, power supply conditioner 100 is incorporated within mobileradio 101 to extract the unwanted noise and provide feed-forwardrejection via the use of an adaptive noise canceller 140 to continuouslyminimize noise on power supply line 105.

In accordance with the embodiment of FIG. 1, power supply conditioner100 includes a first DC block 110, shown as a capacitor, coming off ofmain power supply line 105 and leading to a threshold detector 120 andprocessor 190 for extracting unwanted noise 115 above a certainthreshold and providing it to an adaptive noise canceller 140 inaccordance with the embodiment. Threshold detector 120 monitors the rawsupply voltage line 105 for ripple/noise, and once the ripple/noiseexceeds a predetermined threshold(s), processor 190 enables the adaptivenoise canceller 140. In accordance with the embodiment, adaptive noisecanceller 140 takes the noise signal 115 and generates a cancellationsignal 145 having a same amplitude but opposite phase of noise signal115. A power supply interface device 160, such as implemented withstandard transistors, high power op amps or other interface devices,combines the raw direct A+ signal 105 with the cancellation signal 145to provide a minimized error signal 165. The minimized error signal 165,which is also the output of the power supply conditioner 100, isprovided to both the mobile radio circuitry 103 as well as being fedback through a second DC block 170, shown as a capacitor, to filter outerror remaining on the output and providing this filtered error 175 backto the adaptive noise canceller 140.

Adaptive noise canceller 140 may be implemented in hardware or software.For illustrative purposes, the adaptive noise canceller 140 is shown asa separate block, however for certain applications, such as digitalapplications, the adaptive noise canceller may be configured within adigital signal processor. Functionally, adaptive noise canceller 140updates filter coefficients 142 for use at adaptive filter 144. Inaccordance with the embodiment, the adaptive noise canceller 140 takesthe error signal 175 along with current noise conditions to acoefficient update block 142 for use in adaptive filter 144. The updatedcoefficients are used as filter coefficients for adaptive filter 144 toadaptively filter incoming noise signal 115. The updated coefficientsare used to produce an updated cancellation signal 145 for adaptivelyminimizing the noise on power supply line 105. The cancellation signal145 is continuously updated based on current noise conditions. Thus,power supply conditioner 100 in accordance with the embodiment providesfeed-forward rejection via the use of adaptive noise canceller 140 tominimize unwanted noise on power supply line 105. The continuousupdating provides an adaptive system which is able to removetime-varying noise from the power supply line 105.

The embodiment of FIG. 1 is shown in a digital application and thus, thepower supply conditioner 100 further includes analog to digital (A/D)converters 130 and 180, and a digital to analog (D/A) converter 150. Thepower supply conditioner 100 may just as easily operate in an all-analogenvironment without the use of the converters as will be discussed laterin conjunction with FIG. 3. The adaptive noise canceller 140 andconverters 130,150 and 180 are preferably deactivated when theripple/noise falls below the predetermined threshhold(s) to minimizepower consumption in low noise environments, with power supply interface160 simply providing the raw A+ signal directly to the mobile radiocircuitry 103.

While the embodiment described in conjunction with of FIG. 1 uses athreshold detector 120 and processor 190 for noise detection, otherdevices such as a sensor could also be used. The processor 190 ispreferred however, because the processor already exists as part of themobile radio circuitry 103. The implementation of power supplyconditioner 100 of the embodiment can be incorporated into a mobileradio design without significant cost and very few additional componentsby using the mobile radio's existing processor in conjunction with anoise cancellation technique providing adaptive filtering in a feedforward configuration.

Different adaptive filtering techniques can be used in the adaptivenoise canceller 140 to reduce unwanted noise. For example, for rippledistortions, the power supply conditioning for sinusoidal noise may beobtained by using a Least Mean Squared (LMS) adaptive technique. In theLMS technique, the coefficients for the adaptive filter are updatedbased on the current noise conditions. The coefficients of the adaptivefilter 144 are updated using the processor 190 to minimize the meansquare value of the error signal. In other applications, a Recursiveleast squares (RLS) adaptive technique may be applied for other varyingnoise conditions. The adaptive noise canceller 140 operating inaccordance with the present invention, whether embodied using LMS, RLSor some other technique, is applied in a feed-forward configuration togenerate a cancellation signal 145 that is continuously updated.

FIG. 2 is a flowchart of a method 200 for minimizing noise on a supplyline of a mobile radio in accordance with an embodiment of theinvention. Method 200 reduces the noise on the power supply line 105while simultaneously reducing the power requirement for the power supplyconditioner 100. At step 202, power supply conditioner 100 starts bymonitoring the noise on the power supply line 105. In step 204, thepower supply conditioner 100 determines if the noise exceeds a thresholdvalue. If the noise falls below the threshold value, then a step ofproviding the supply line signal directly to the mobile radioelectronics occurs at 206, followed by the return to step 202 formonitoring of the power supply line 105. Hence, steps 202, 204, and 206of method 200 are repeated and the adaptive power conditioning isdisabled for reducing the power requirement in low noise environment.

If the noise is above or equal to the threshold value, step 208 isinitiated for conditioning the supply line signal. In step 208, the DCcomponent of the supply line signal is blocked to extract the noise.Subsequently, the noise may be digitized for power supply conditioningimplemented on digital systems. This is followed by step 210, whereinfiltering of the noise is performed using adaptive filter 144 forgenerating a cancellation signal. Step 212 involves combining thecancellation signal with the supply line signal to generate an outputsignal. Additionally, in a digital system, the cancellation signal maybe converted to an analog signal before being combined with the supplyline signal. This is followed by extracting an error signal from theoutput signal by blocking the DC component in step 214. Finally,updating of the cancellation signal is performed in step 216 based onupdated filter coefficients of the adaptive filter 144. The updating offilter coefficients is performed using the current noise conditions andthe error signal. In the present embodiment, the steps 208 through 216are repeated while the noise is above or equal to the threshold value.Repeating of steps results in an adaptive system which is able to removetime-varying noise from the power supply line 105. Whenever the noisefalls below the threshold value, the power supply conditioner returns tostep 202 and performs the steps of method 200 as required.

FIGS. 3, 4 and 5 are provided to show an example of an embodiment of thepower supply conditioner under simulated conditions. FIG. 3 is aschematic of a simplified power supply conditioner 300 in accordancewith a simulated analog embodiment of the invention. FIG. 4 provides agraph 400 of simulated input having noise generated thereon for use inthe schematic simulation of FIG. 3. FIG. 5 shows a graph 500 ofsimulated output with minimum noise thereon as generated by theschematic simulation of FIG. 3. The schematic and graphs are provided asa visualization of improvement in noise minimization achievable with apower supply conditioner formed in accordance with this embodiment.

As FIG. 3 represents an analog embodiment, power supply conditioner 300lacks the converters 130,150 and 180 of FIG. 1. The simplified powersupply conditioner 300 was used for obtaining simulation results undervarying noise conditions. For simulation purposes, a DC blockingcapacitor of 10 μF was used as a signal conditioner 310. The main powersupply 302, A+ was set to 13.8V, and coupled to the power supplyinterface device 360. The output 365 from the power supply interfacedevice 360 was coupled to DC block filter 370. In the simulationembodiment, the DC block 370 was implemented using a capacitor of 10 μF.Error signal 375 from the DC blocking capacitor 370 was fed back to theadaptive noise canceller 340 along with the DC blocked output from thefirst Dc blocking capacitor 310 to generate an updated cancellationsignal 345. The cancellation signal 345 was combined with the noisy rawA+ to produce output 365 for the mobile radio 301.

FIG. 4 shows the power supply line input simulation for use at input 302of FIG. 3. The graph 400 represents raw voltage supply along the y-axisand time along the x-axis. Besides 13.8V supply voltage, the raw A+input 402 includes a 1 kilohertz, 1V peak-to-peak sinusoidal noisecomponent. FIG. 5 shows the output signal 565 obtained at 301 of FIG. 3.Graph 500 represents output voltage supply along the y-axis and timealong the x-axis. Graph 500 illustrates the simulated output 565 for thepower supply conditioner 300 in response to the raw A+ input 402. It isobserved that, as time passes, the output 565 rapidly converges towardsthe ideal Raw A+ voltage of 13.8V and sinusoidal noise component getsnegligibly small. The simulated convergence time is less than 10 mS. Thesimulated reduction in the noise is found to be 20Log (0.064V/1.0V) orapproximately 24 dB. Different mobile radio designs, noise levels,component values, threshold levels, etc. can all be optimized fordifferent operating environments.

As mentioned previously, various implementations of the power supplyinterface device are possible in the described embodiments. The powerinterface device 160 of FIG. 1 may be an operational amplifier receivingthe supply line input at one node and the cancellation signal at theother. FIG. 6 is an example of a power interface device in accordancewith some embodiments of the invention. The power supply bus interfacedevice 600 comprises a pass transistor 610, a driver transistor 615, abias transistor 620, resistors 622, 625, 630, 635, 650, and 655, and ahigh power resistor 640. The pass transistor 610 has sufficient currentgain to force the cancellation signal 645 (corresponding to 145 ofFIG. 1) onto the supply line 605 (corresponding to supply line 105 ofFIG. 1) for values up to the maximum expected amplitude of the unwantednoise component. It is also capable of handling the full rated supplycurrent requirements of the supply line. The driver transistor 615 isused for driving the pass transistor 610. It has sufficient current gainto drive the pass transistor 610 in order to force the cancellationsignal 645 onto the supply line. The bias transistor 620 acts as aswitch to bias the driver transistor with the cancellation signal 145.It is also used to drive the pass transistor 610. Resistors 622, 625,630, 635, 650, and 655 are used as biasing devices for the transistors610, 615 and 620 for resulting in the required current gain. The highpower resistor 640 is coupled to the output 675 (corresponding to 165 ofFIG. 1) and is capable of handling large currents. As mentionedpreviously, other power supply interface device configurations can beused to combine the raw direct A+ signal with the cancellation signal toprovide a minimized error signal.

Accordingly, there has been provided a power supply conditionerparticularly useful for mobile radios mounted in a vehicle. The powersupply conditioner of the present invention avoids the use of hugecapacitors and inductors and thus achieves compact and robust design fora mobile radio's power supply. By utilizing the adaptive power supplyconditioning scheme of the present invention, problems associated withtime varying noise are avoided and fast noise cancellation on raw powersupply is achieved. The power supply conditioner may be embodied on adigital signal processor for a digital implementation which may furthersimplify design. The use of a threshold detector in conjunction with theradio's processor significantly reduces the power consumption of thepower supply conditioner for low noise environments.

In the foregoing specification, specific embodiments of the presentinvention have been described. However, one of ordinary skill in the artappreciates that various modifications and changes can be made withoutdeparting from the scope of the present invention as set forth in theclaims below. Accordingly, the specification and figures are to beregarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope ofpresent invention. The benefits, advantages, solutions to problems, andany element(s) that may cause any benefit, advantage, or solution tooccur or become more pronounced are not to be construed as a critical,required, or essential features or elements of any or all the claims.The invention is defined solely by the appended claims including anyamendments made during the pendency of this application and allequivalents of those claims as issued.

1. A method for minimizing noise in a mobile radio of a vehicle, comprising the steps of: generating a supply line signal from a power supply within the vehicle; conditioning the supply line signal for the vehicle by extracting unwanted noise; filtering the unwanted noise to generate a cancellation signal having same amplitude but opposite phase of the unwanted noise; combining the cancellation signal with the supply line signal to generate an output signal; extracting an error signal from the output signal; and updating the cancellation signal based on the error signal and current noise conditions while supplying the output signal to an input of the mobile radio.
 2. The method of claim 1, further comprising repeating the steps of conditioning through updating while the unwanted noise is above a threshold value.
 3. The method of claim 1, further comprises outputting the supply line signal directly to the input of the mobile radio, if the unwanted noise falls below a threshold value.
 4. The method of claim 3, further comprises: monitoring the unwanted noise on the supply line signal; and repeating the steps of conditioning through updating if the unwanted noise is above the threshold value.
 5. The method of claim 1, wherein the step of conditioning further comprises blocking a DC frequency component in the supply line signal to extract the unwanted noise.
 6. The method of claim 1, further comprising a step of digitizing the unwanted noise after the step of conditioning.
 7. The method of claim 6, further comprising a step of converting the cancellation signal from a digital signal to an analog signal prior to the step of combining.
 8. The method of claim 7, further comprising a step of digitizing the error signal after the step of extracting.
 9. The method of claim 1, wherein the step of extracting the error signal further comprises blocking a DC frequency component of the output signal.
 10. The method of claim 1, wherein the step of updating further comprises determining coefficients of an adaptive filter so that a mean square of the error signal is minimized.
 11. An apparatus for minimizing noise in a mobile radio of a vehicle, comprising: a signal conditioner receiving an input from a supply line generated from an output of a power supply for the vehicle, the signal conditioner for extracting unwanted noise; an adaptive noise canceller receiving the unwanted noise and generating a cancellation signal; a power supply interface device combining the cancellation signal to the supply line for producing an output signal; and a feedback path extracting an error signal from the output signal and providing the error signal to the adaptive noise canceller.
 12. The apparatus of claim 11 further comprising: a threshold detector for detecting when the unwanted noise exceeds a threshold value; and a processor for enabling the apparatus in response to the detector detecting that unwanted noise exceeds a threshold value.
 13. The apparatus of claim 11, wherein the signal conditioner comprises a first capacitor for filtering unwanted noise from the input.
 14. The apparatus of claim 13, further comprising an analog to digital converter for digitizing of the unwanted noise.
 15. The apparatus of claim 14, further comprising a digital to analog converter for converting the cancellation signal to an analog signal for the power supply interface device.
 16. The apparatus of claim 14, wherein the feedback path farther comprises an analog to digital converter for converting the error signal to a digital signal for the adaptive noise canceller.
 17. The apparatus of claim 11, wherein the adaptive noise canceller comprises an adaptive filter and a processing means used to minimize mean square of the error signal.
 18. The apparatus of claim 11, wherein the power supply interface device comprises: a pass transistor coupled along the supply line to force the cancellation signal on to the supply line; a driver transistor coupled to a control gate of the pass transistor for enabling the pass transistor; a bias transistor for receiving the cancellation signal and biasing the driver transistor with the cancellation signal; a plurality of bias resistors coupled to the driver transistor, the bias resistors and the bias transistor for generating sufficient current for driving the cancellation signal onto the output; and a high power resistor for coupling output of the pass transistor as the output.
 19. The apparatus of claim 11, wherein the power supply interface device includes an operational amplifier.
 20. The apparatus of claim 11, wherein the feedback path includes a second capacitor for filtering error from the output signal and presenting the error signal to the adaptive noise canceller.
 21. A vehicle, comprising: a mobile radio mounted within the vehicle; a plurality of electromechanical components; a main DC power supply powering the plurality of eletromechanical components and the mobile radio, the main power supply having a power supply line with unwanted noise generated thereon by the plurality of electromechanical components; an adaptive power supply conditioner within the mobile radio, the adaptive power supply conditioner detecting unwanted noise on the power supply line and generating an inverse cancellation signal in response thereto, the adaptive power supply conditioner combining the inverse cancellation signal with the unwanted noise on the power supply line powering the mobile radio; and wherein the inverse cancellation signal combined with the unwanted noise provides an output signal, the output signal having error extracted therefrom, the error being fed back to the adaptive noise canceller, and wherein the inverse cancellation signal is continuously updated based on current noise conditions and the error extracted from the output signal. 